The present invention relates to interventional catheters, and more particularly to stent delivery systems and methods.
The treatment of an occluded region of a patient's vasculature commonly includes a percutaneous transluminal interventional procedure such as inflating a catheter balloon and/or implanting a stent inside the blood vessel at the site of the stenosis. For example, in balloon angioplasty, the catheter balloon is positioned across the lesion and inflated with fluid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to clear the passageway. Physicians frequently implant a stent inside the blood vessel at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel.
Conventional stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of a catheter balloon or other expansion means on which the stent is mounted, which expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type is a self-expanding stent, formed, for example, of shape-memory metals such as super-elastic nickel titanium (NiTi) alloys which will automatically expand from a compressed state when the stent is displaced from the restraining force of the delivery catheter system.
Delivery and deployment of balloon expandable stents at a desired location within the patient's body lumen typically involves advancing a stent delivery balloon catheter through the patient's vascular system until the balloon with the stent mounted thereon is positioned within the treatment area, and then inflating the balloon to expand the stent within the blood vessel. The balloon is then deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel, holding open the passageway thereof. In contrast, implanting self-expanding stents within the patient's vasculature typically involves a method which is different than the one for non-self-expanding stents, and in which the stent expands upon the removal of the force of a radially restraining member. For example, some prior art stent delivery systems for self-expanding stents include a catheter with an inner tubular member upon which the compressed or collapsed stent is mounted, and an outer restraining sheath which is positioned over the compressed stent prior to deployment. When the catheter is in position in the body lumen, the outer sheath is moved in relation to the inner tubular member of the catheter to uncover the compressed stent, allowing the stent to radially self-expand to its expanded condition. Some delivery systems utilize a “push-pull” technique in which the outer sheath is retractable while the inner tubular member is pushed forward or held in place. Still other systems use an actuating wire which is attached to the outer sheath. When the actuating wire is pulled to retract the outer sheath from over the collapsed stent, the inner tubular member must remain stationary, preventing the stent from moving axially within the body vessel. Thus, such self-expanding stents can typically be at least partially expanded without the need for application of a controlled force on the stent, such as is applied through the inflation of the balloon portion of a balloon catheter. However, self-expanding stent delivery systems have been suggested in which inflation of a balloon is required to deploy the self-expanding stent, for example where the balloon is inflated to break or otherwise release the radially restraining member (e.g., outer sheath) from around the collapsed stent.
Implanting the stent may release emboli into the circulatory system, which can be extremely dangerous to the patient. Debris that is carried by the bloodstream to distal vessels of the brain may cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Thus, when performed in a carotid artery, an embolic protection device to capture and collect released emboli may be deployed downstream to the interventional catheter. For example, embolic protection devices in the form of filters or traps can be delivered in a collapsed configuration to a location adjacent to the interventional procedure site, radially expanded to open the mouth of the filter or trap, and after the interventional procedure has been performed, the device is collapsed for removal with the captured embolic material therein.
An essential step in effectively performing an interventional procedure is properly positioning the catheter system at a desired location within the patient's vasculature. The catheter shaft must be able to transmit force along the length of the catheter shaft to allow it to be pushed through the vasculature. However, the catheter shaft must also retain sufficient flexibility and low profile to allow it to track over a guidewire through the often tortuous, narrow vasculature. Such deliverability issues must be balanced against one another and against other performance characteristics. As a result, one design challenge has been making the procedure, including the delivery and retrieval of the components of the catheter system, as quick and easy as possible.